Sound absorbing material

ABSTRACT

To satisfy the fire protection requirements for a sound-absorbing material, especially in the form of open-cell foam, without impairing the acoustic properties, at least a part of the surface of the sound-absorbing material, which is covered with an acoustically transparent film, is coated with a flame-retarding powder or sprayed with a flame-retarding solution.

The invention relates to sound-absorbing material used, for example, as a lining for the engine space of vehicles, in particular for public means of transport. Such sound-absorbing material is also used for railway carriage walls of rail vehicles and in the fuselage area of aeroplanes.

It is known to use open-cell foam material for reducing the sound level in the engine space of vehicles. Thickness and material properties like porosity determine the reduction in sound level to be achieved.

According to recent directives, sound-damping material (sound insulation) must satisfy strict fire protection requirements, especially in public means of transport, and frequently a thermally insulating property is also required, wherein dewpoint problems cause particular difficulties which cannot be solved using open-cell foams.

Although sealed or dense foams dam the sound, they do not attenuate or reduce the sound and are thus acoustically unsuitable for the engine space. On the other hand, for fire protection there is a given requirement for denser surfaces which neither let fire accelerants such as oil or fuel through, nor hold them on the surface

Porous foam material can be sealed up by means of films. If thin acoustically transparent films such as polyurethane films are used, then the acoustic requirements can be met, but the fire protection requirements cannot, because in the mandatory fire test 95/28 EC (Directive of the European Community) these films become ablaze.

Non-flammable films do exist. Nevertheless, when some films which are classified as non-flammable are applied to porous foam, such as melamine resin foam, which is fire-proof, the film still burns due to the porosity of the foam. It is known that particular fire-proof materials do burn in combination due to a mutual catalytic effect. However; all of the films which in fact are non-flammable even in combination with foam material, have the properties of being sound-proof and stiff, so they are not serviceable with regard to protection from sound.

All in all, therefore, the requirements made on sound-absorbing material are mutually exclusive.

The invention is based on the object of forming sound-absorbing material such that it meets sound protection requirements on the one hand and fire protection requirements on the other.

This object is solved according to the invention by the features in claim 1. By strewing the surface of the porous absorber material, preferably melamine resin foam, with flame-retarding powder or spraying it with a flame-retarding solution, effective fire protection is achieved without impairing the sound-absorbing properties of the material, wherein penetration of the absorber by fuel or suchlike inflammable material is prevented by the acoustically transparent film.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing, in which

FIG. 1 shows a schematic cross-section of a layer of foam with a powder coating under a film cover, and

FIG. 2 shows a section through a modified embodiment.

In FIG. 1, a layer 1 of sound-absorbing material is strewn with flame-retarding material 2 in powder form, or coated by spraying, at least on the part of the surface to be protected from the development of a fire. The sound-absorbing material 1 preferably consists of melamine resin foam; however, it can also consist of polyurethane foam layers, fleece layers, felt layers or mineral fibre layers. The flame-retarding material 2 used can consist of standard products like swollen graphite and/or of products based on nitrogen and phosphorus, which remove oxygen or heat from their surroundings under temperature influence and thus prevent flames developing on the surface of the absorber material.

An acoustically transparent film 3 is arranged over the layer of flame-retarding powder 2 or of a corresponding sprayed-on solution. The film 3 itself can burn in the case of fire; however, due to the flame-retarding powder 2 present between film 3 and absorber surface, any flame sparked by the film will be quenched.

By using an acoustically transparent film 3, the sound absorbing properties of the porous absorber material 1 are preserved. Further, the acoustic properties can be adjusted by the choice of type of film. The flame-retarding powder 2 applied to the absorber surface does not impair the acoustic properties of the absorber material.

It is preferable to use films which are adjusted to be of low flammability in themselves. If, however, the film 3 were still to burn due to a catalytic effect of the porous sound-absorbing material 1, the flame would be quenched by the flame-retarding coating material 2

To fix the powder material on the foam surface, the powder can be mixed with adhesive before application. According to another embodiment, the flame-retarding powder 2 can also be fixed by surface-fusing the surface of the film and/or that of the absorber 1.

The grain size of the flame-retarding powder 2 is preferably selected such that it cannot easily penetrate the pores of the foam material. When the sound-absorbing material is used, for example, in the engine space of a vehicle, it is exposed to vibrations by means of which the flame-retarding powder 2 could penetrate the pores of the absorber material 1 and so lose its flame-retarding effect on the surface. To prevent this, the grain size of the powder can be selected in relation to the porosity of the absorber material such that penetration of the pores is prevented. Additionally or alternatively, the powder material is fixed on the surface of the absorber material or on the surface of the film 3 for example by an adhesive or by surface-fusing, such that no displacement of the powder material 2 can result from the vibrations. Here, it is not necessary for the flame-retarding powder 2 to form a closed layer.

The absorber material 1, which is strewn with flame-retarding powder 2 or sprayed with a corresponding solution, can be formed according to the requirements of shape by stamping, cutting or in another way, so that it can be used as a lining, for example in an engine space.

Due to the different and partly very complicated design for the lining, for example, of an engine space, three-dimensional deformation of the sound absorber is frequently required, for example, a concave or convex design or one provided with a shoulder, so that the sound absorber can be adapted to the given shape

The absorber material 1 strewn with flame-retarding powder or sprayed with flame-retarding solution and cut as desired, is surrounded on the front side and advantageously also on the edges by a deformable acoustically transparent film, preferably of polyurethane. Here, a flame-retarding coating 2 is provided, preferably in the whole area covered by the film 3. If the absorber material 1 covered in this way by a film 3 is adhered, for example, to a non-flammable carrier material, for example, a metal wall, then the rear side of the absorber material 1 can remain free of coating 2 and/or of a film covering. However, if the absorber material is only inserted, for example, in the paneling of a vehicle, then the absorber material 1 is encased in the film 3 on all sides. On account of the risk that the film itself could burn, a flame-retarding coating 2 is also provided on the rear side between film and absorber material, that is, in the whole area covered by the film. Because the absorber material is completely covered, no oil or fuel can penetrate the absorber material from any side. The film is preferably applied to the absorber material by heat-shrinking, wherein three-dimensional deformation can be carried out.

In the case of absorber material 1 being completely encased in an acoustically transparent film 3, the dewpoint problem is also solved, as the surfaces are tightly sealed. Thus the absorber material meets all the requirements regarding fire protection, noise protection and thermal properties.

It is also possible to apply the flame-retarding powder to an acoustically transparent film by means of an adhesive or by surface-fusing, before the film is applied to the sound-absorbing material 1.

According to a modified embodiment, it is also possible to apply the flame-retarding powder 2 or a sprayed-on solution to the outside of the film 3, in addition to a coating 2 between film 3 and absorber material 1 or instead of the coating 2 provided between film 3 and absorber material 1.

A coating or a sheet-like structure which foams under temperature influence and forms an insulating layer, can also be provided as flame-retarding material 2.

The absorber material 1 can be provided with a surface structure, for example, with concave and convex areas offset from one another. For such a material with a surface structure, the film can extend over the concave areas of the surface structure, wherein the flame-retarding material 2 is preferably fixed to the film.

FIG. 2 shows an embodiment in which a fleece 4 is arranged between flame retardant 2 and foam material 1. In another embodiment, a fleece 4 can be provided between film 3 and flame retardant 2

By means of a fleece 4 on the one and/or other side of the layer of flame-retarding material 2, a further improvement in the sound insulation and flame-retarding properties can be achieved. Here, the flame-retarding material 2 can also be incorporated in the fleece.

The embodiment according to the invention can be used in many ways and not only in public means of transport, for different absorber materials such as felt or fleece, and with the most different designs. 

1. Sound-absorbing material, especially in the form of open-cell foam, which is covered by an acoustically transparent film (3) wherein at least a part of the surface of the sound-absorbing material is coated with a flame-retarding powder (2) or sprayed with a flame-retarding solution
 2. Sound-absorbing material according to claim 1, wherein the flame-retarding powder is mixed with adhesive.
 3. Sound-absorbing material according to claim 1 or 2, wherein the film (3) completely encases the absorber material (1)
 4. Sound-absorbing material according to one of the preceding claims, wherein the layer of flame-retarding material (2) is arranged between the acoustically transparent film (3) and the absorber material (1).
 5. Sound-absorbing material according to one of claims 1 to 3, wherein the flame-retarding coating (2) is applied to the outside of the acoustically transparent film (3).
 6. Sound-absorbing material according to claim 4 or 5, wherein a fleece (4) is arranged on the one and/or on the other side of the layer of flame-retarding material (2).
 7. Sound-absorbing material according to one of claims 1 to 3, wherein the flame-retarding material (2) is incorporated in a fleece (4) which is arranged between the acoustically transparent film (3) and the foam material (1). 